A motor-vehicle wheel is typically mounted so that it can move vertically relative to the frame of the vehicle, and a spring urges the wheel downward. A shock absorber is braced vertically between the wheel and the vehicle frame and comprises a piston having a piston rod normally pivoted on the frame and a cylinder pivoted on the wheel. The piston defines in the cylinder a pair of liquid-filled compartments and an orifice is provided for fluid flow past the piston between the compartments. Thus vertical movement of the wheel is damped in that liquid flow between the compartments is throttled so that the shock absorber prevents the wheel from moving relative to the frame at too great a speed. This damping improves the ride of the vehicle.
It is considered desirable to increase the damping effect at the upper limit of travel of the wheel relative to the vehicle frame, so that as the wheel is being moved up to a point where its spring and the shock absorber will bottom, transmitting force directly from the wheel to the frame, such upward displacement will be resisted with increasing force. This can be done simply by putting a rubber bumper at one end of the shock absorber as described in British patent 1,085,157 of D. Gladstone. Such an arrangement has the considerable disadvantage that the force/stroke curve increases regularly so that extreme jolts are transmitted to the vehicle frame, and the stored-up energy is retransmitted back to the wheel suspension later. In both cases this can damage the suspension.
It is also known to provide an end damper that somewhat overcomes this problem as described in German patent document 2,445,250 filed Sept. 21, 1974 by W. Zenz by providing a second piston and spring in the shock absorber, or by changing the flow cross section of the passage communicating between the compartments of the shock absorber as described in German patent 969,377 of B. Barenyi. Other more complex arrangements are seen in U.S. Pat. No. 3,036,669 of H. Schultze, German patent document 3,328,300 of J. Hardt (based on a Swiss priority of Jul. 20, 1983), and Japanese patents 62-64603 and 62-64604 both of Y. Kubot.
None of these more complex hydraulic arrangements provides a flat force/stroke curve. Thus there remains a potential of damage to the wheel suspension structure.